Background: Shift workers who experience sleep disturbances and exposure to light at night
could be at increased risk for alterations in physiologic functions that are circadian in nature.
Methods: We investigated rotating shift work and menstrual cycle patterns in the Nurses'
Health Study II using cross-sectional data collected in 1993 from 71,077 nurses aged 28–45
years who were having menstrual periods and were not using oral contraceptives. Log-
binomial regression was used to estimate relative risks (RRs) and 95% confidence intervals�…